The purpose of the present work is twofold. On the one hand, it attempts to provide a critical exposition of the ethical theory of Jean-Paul Sartre. On the other hand, it strives to explain, and in a limited way to defend, the central thesis of that theory, namely, that freedom is the "highest," or most important, value. ;The study begins with an extensive discussion of Sartre's theory of freedom. Sartre's arguments for the freedom of consciousness are identified and presented, and a number of widespread misunderstandings of Sartre's conception of the nature of freedom are corrected. Specifically, it is argued that, contrary to prevailing opinion, Sartre distinguishes between different senses of freedom, insists that freedom is always limited, and remains substantially consistent, throughout his intellectual career, in his understanding of the nature of freedom. ;The study next takes up Sartre's theory of values. Here the well-known strain of ethical subjectivism in Sartre's thought is presented and criticized, with the main instrument of criticism being a distinction, overlooked by Sartre, between subjectivism as a meta-ethical theory about the status of moral judgments, and subjectivism as an ontological doctrine regarding the existence of moral values. ;The study concludes with an explanation and defense of the theory that freedom is the highest value. Here the presentation of Sartre's ethical theory is brought to completion through a discussion of its neglected objectivist elements, and through a development in regard to ethics of Sartre's general theory of knowledge. It is then shown that the notion of freedom as a value underlies both the subjectivist and the objectivist phases of Sartre's ethical thought, and it is suggested that these two phases can be reconciled in a conception of ethics as a dialectic of invention and discovery. This conception is defended by way of a brief discussion of its advantages over rival ethical theories, which neglect one or the other of the stages of this dialectic